The leak of an arrest warrant to far-right groups has heightened widespread suspicions of links between German police and xenophobic demonstrators.

Authorities have confirmed reports of the leak after the arrest warrant – containing the full name of the main suspect in the murder of a 35-year-old man, which triggered violent anti-foreigner protests in the eastern city of Chemnitz – was tweeted by Lutz Bachmann, the founding member of the far-right protest group Pegida. The suspect is a 22-year-old Iraqi man.

Police in Chemnitz are under fire for being inadequately prepared for far-right protests in the city on Sunday night, following the stabbing of Daniel H, whose surname has not been released in line with German practice.

The demonstration attracted around 6,000 people and 1,500 counter-protesters and quickly turned violent with far-right groups breaking off into smaller mobs and hunting foreigners through the city streets in riots that continued on Monday evening. Some protesters shouted: “For every dead German, a dead foreigner,” in scenes reminiscent of Nazi-era pogroms.

A police spokeswoman confirmed the authenticity of the arrest warrant to German media. “The document is real,” she said. “We have already instigated a judicial inquiry ... regarding the violation of official secrets.”

The photo of the arrest warrant was quickly circulated online, in particular via a WhatsApp group of the far-right movement Pro Chemnitz, which originally called the demonstration on Sunday.

Martin Dulig, the deputy premier of Saxony state, called the leak scandalous. “To hear that the arrest warrant was probably leaked by the police to rightwing extremist circles means that we have a huge problem to deal with. This is an egregious occurrence,” the SDP politician said.

The leak has fuelled existing concerns about links between Saxony’s police force and the anti-immigrant party Alternative für Deutschland and the Pegida protest movement, which has led to an increasing use of the nickname “Pegizei” to describe the police – a portmanteau of polizei police and Pegida.

The police were accused last week of standing up for Pegida protesters after stopping a camera team from the state broadcaster ZDF from filming a demonstration in Dresden for 45 minutes after complaints by a protester, who it later emerged was a police employee.

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They faced further accusations on Wednesday that they had lied over their claim to have underestimated the numbers who would attend the Chemnitz demonstration, after it emerged that Saxony’s office for protection of the constitution had warned them in advance that a large number of extremists from across Germany – including neo-Nazis, as well as football hooligans and martial artists with a known far-right background – were expected in the city, in the “low to medium four-figure realm”.

Around 591 officers were deployed, a figure police chiefs later admitted had been totally inadequate.

Following Sunday and Monday’s riots, Chemnitz was quiet on Tuesday evening, but Michael Kretschmer, Saxony’s premier, said he expected the protesters would want to build on the momentum they had created, and would continue to call further rallies.

He said he was confident, however, that security forces were ready for a demonstration called by Pro Chemnitz in the city on Thursday.

“We will make it clear that the state has the monopoly on the use of force,” he said, promising a tougher line compared with earlier in the week on demonstrators who habitually use the Hitler salute, which is outlawed.

Kretschmer described the fight against the far right as “a battle which we will win”. He said Chemnitz had become increasingly attractive for the far-right movement and a central focus point for its mobilisation, in part because of the widespread media attention given to demonstrations there.

Germany’s leadership is desperately seeking strategies to deal with the political fallout from the events in Chemnitz, which are largely being blamed on Angela Merkel’s refugee policy. Her Christian Democrat party (CDU), which has held power in Saxony since 1990, is widely accused of failing to recognise or effectively confront the growing far-right movement.

The state faces a crucial election next year in which the CDU could lose 10% of its support to Alternative für Deutschland, according to current opinion polls. The AfD, which has been quick in the last few days to exploit the xenophobic mood in Chemnitz, mainly via social media, is on course to gain as much as 25% of the vote, which could make it the second largest party in the state parliament.

Former states of the communist German Democratic Republic such as Saxony have never come to terms with the presence of the far right, having inadequately tackled the legacy of the Nazi era under communism.

Chemnitz, a former industrial hub during communism called Karl Marx Stadt, has struggled economically in recent years, suffering from high unemployment and a loss of around 80,000 of its citizens – more than 20% – to migration since reunification.